In general, a vacuum insulating panel is formed of a fine porous insulating material and has a very low thermal conductivity. An interior material of the vacuum insulating panel is fumed silica and is surrounded by a multilayered film coated with aluminum. The interior of the vacuum insulating panel is evacuated to provide excellent thermal conductivity.
In measurement of the degree of vacuum of the vacuum insulating panel, a pressure sensor is directly inserted into the vacuum insulating panel. However, this method is a destructive examination and is not suitable for measurement of the degree of vacuum of a mass-produced product.
Therefore, there is a need for a method and apparatus capable of more easily measuring the degree of vacuum of a multistage vacuum heat-insulating panel.